1. Field of the Invention
This invention relates to the production of highly specific antibodies to human chorionic gonadotropin (hCG). These antibodies, produced in vivo by rats or in vitro by rat lymphocyte hybridomas, are useful in quantitating the levels of hormone in the blood of individuals as an indicator of pregnancy.
2. Description of the Prior Art
Chorionic gonadotropin is a hormone that is normally present in very low levels in the serum. Early in pregnancy the serum levels of hCG rise dramatically. This increase in hCG level can be measured by immunoassay procedures, which are the most common form of pregnancy test.
Commercially available immunoassays for hCG make use of either antisera from rabbits (polyclonal) or monoclonal antibodies derived from mouse hybridoma cells (Kohler and Milstein, Nature, Vol. 256, 495-7, 1975). For these assays to accurately measure hCG, the antibodies used in them must not cross react with other related hormones such as luteinizing hormone (LH), thyroid stimulating hormone (TSH), or follicle stimulating hormone (FSH). All four hormones have identical .alpha.-subunits and similar .beta.-subunits. As a result of the similarities, rabbits or mice immunized with intact, unmodified hCG molecules often produce antiserum (or in the case of mouse hybridomas, monoclonal antibodies) with unacceptably high cross-reactivity to the other hormones mentioned. When purified .beta.-subunit of hCG is used for immunizations, as in Domini U.S. Pat. No. 3,992,514 or Tsong et al. U.S. Pat. No. 4,271,069, the animals still produce antibodies with significant cross-reactivity.
Alteration of the hCG molecule by conjugation to other molecules or by chemical means, as proposed by Tawar et al., PNAS, U.S.A., Vol. 72, 218-222 (1976); Bahl et al., Biochem. Biophys. Res. Comm., Vol. 70, 525-532 (1976); Pappenhagen et al. U.S. Pat. No. 3,903,262; or Bahl U.S. Pat. No. 4,234,561, often results in a molecule with reduced immunological activity yielding low titer, low affinity antibodies. In addition, these and other methods of hCG modification require significant technological effort and expense to produce an altered hCG molecule for immunization.